Resilience of mediterranean shrub communities to fires

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Abstract

All mediterranean shrub communities are resilient to wildfires at a frequency range of every 20–50 years. These communities, however, are not unique in this respect. Many non-mediterranean shrub communities are dominated by species capable of resprouting and thus are resilient to occasional wildfires. Certain mediterranean shrub communities are unique in that they are dominated by species which have specialized their reproductive cycle to fires. These species recruit seedlings only in the first postfire year and since the burned shrubs are incapable of vegetative regeneration, they are referred to as obligate seeding shrubs. Such species require fires for rejuvenation and population expansion. Communities dominated by obligate seeding species are not resilient to wide deviations from this modal fire frequency. Fires at shorter intervals readily eliminate species with this life history mode. Likewise, extremely long intervals between fires could eliminate such species, though the upper limit of tolerance is unknown. California chaparral obligate seeding shrubs are largely resilient to fire-free intervals of 100 years or more but this may not be universally true for obligate seeding shrubs in other regions. Mediterranean-climate shrub communities dominated by resprouting shrubs are resilient to a much shorter fire recurrence interval. Certain of these species however fail to establish seedlings after fire and it appears that these obligate resprouters require extended fire-free periods for seedling establishment. Many of these resprouting species are capable of continually rejuvenating their canopy by sprouting from the base and there is reason to believe that communities dominated by such species would be resilient to very long fire recurrence intervals. The abundance of species with different life history modes varies between the different mediterranean-climate regions as well as along geographical gradients within regions. Thus, resilience of these communities is spatially variable.